Tooling systems, including die and punch assemblies comprising a die set, are mounted in presses and are used for manufacturing numerous products and components of products. The die and punch assemblies are used to cut, punch holes in, shape, or otherwise form material, such as metal, cardboard, plastic, or other stock. The die assembly usually is in the lower or bottom position of the press and the punch assembly in the upper or top position, although the punch assembly may be on the bottom and the die assembly on top. The press, and the die and punch assemblies mounted therein, may be positioned horizontally, vertically, or at an angle. A “blank” of material to be formed, i.e., unshaped material, such as a flat sheet of cardboard or metal, passes between and is clamped by the die and punch and is held in place while the die and punch come together to form the material. The blanks pass between the “front sides” of the die and the punch assemblies, which are the sides facing the blank, as opposed to the “back sides,” which are the sides of the die and punch assemblies facing away from the blank. The die and punch assemblies, or a series of die assemblies and punch assemblies, are activated to form the material into a product or a component of a product, such as a metal hub cap for a car, a paper cup or plate (i.e., pressware formation), or a plastic toy, by example only.
Both the die and the punch assemblies may have knockouts and bushings for holding the blank in place, assisting in the forming or shaping the material, and for knocking the formed product out of the die set. Knockouts commonly have round shafts or stems and may have hardened sleeves pressed into the main shaft diameter. The knockout shaft is slidably disposed within the bushing, which has a lumen or bore for receiving the knockout shaft. A split clamp is clamped around the shaft of the knockout on the back side of the die (the side opposing the front side that faces the blank), which holds the knockout in position relative to the bushing and prevents the knockout from over-extending and sliding out of the front side of the die upon activation. The knockout shaft typically has a reduced diameter at the split clamp location.
In a system having the die assembly as the bottom of the die set, the knockout is activated upwards by pressure (pneumatic, hydraulic, etc.) prior to insertion of the blank, so that the knockout extends upwards towards the blank on the front side of the die assembly. The knockout is fully extended when the split clamp reaches the bushing on the bottom side of the die assembly. When extended, the knockout supports the blank as it enters the die set and in conjunction with the punch assembly, clamps the blank on-center during the blank draw-in, and maintains the blank on-center as the punch assembly forms the product or component. After product formation, the die knockout is deactivated (i.e., the pressure is released) and the knockout slides away from the product, retracting into the bushing as the die set opens, so that the product is not damaged. If the product remains in the bottom half of the die set, the knockout may be reactivated to extend out of the die after the die set has reopened to eject or “knock out” the product and then retract in preparation for receiving the next blank. The knockout is activated upwards as the next blank enters the die set for product formation, and the process described above repeats itself.
The cycling rate of the knockout, meaning the rate at which the knockout extends and retracts or is activated and deactivated within the die assembly, varies with the particular tooling application. Typical values for pressware applications (i.e., the formation of paper plates, bowls, cups, etc.) under normal conditions is one cycle of the knockout every 1–2 seconds, where numerous cycles, in excess of 20 million, can be realized by the knockouts before replacement. Such cycling rates cause wear to the components. Accordingly, both knockouts and bushings usually are made of a strong metal, such as steel or iron, to aid in withstanding the wear. For example, knockouts may be comprised of 1018 steel, and bushings may be comprised of stainless steel, although other materials may be used.
Notwithstanding the strength of the metals, the die set components tend to wear out quickly, particularly the bushing, which is the main wear component. For example, bushings used for pressware applications typically wear out in a matter of three months. Furthermore, knockout shafts tend to break where the split clamp attaches at the portion of reduced diameter due to repeated cycling, heat, and/or excessive loads, such as when the activation pressure is set too high. This wear and breakage results in down time for replacing worn components as well as a loss in product quality as the components wear.
The wear is exacerbated when the press in which the knockout and bushing operate is positioned at an angle or vertically (i.e., the knockout moves horizontally), as opposed to horizontally (i.e., the knockout moves vertically). Even with typical knockout-to-bushing clearances, when the die set is positioned at an angle, the knockout can tip slightly in its extended position. Wear of the knockout or the bushing occurs along a linear portion of the knockout and the bushing due to the friction along the line of contact between the two components, where the linear contact is created by the effect of the angle of the press and gravitational forces. Such linear wear causes the knockout to tip further off-center, resulting in one side of the knockout being higher than the other when extended. As the blank is inserted into the die set, the un-centered knockout that should be supporting the blank may instead tip slightly and prevent the blank from being drawn in or properly aligning between the die and the punch assemblies. Furthermore, even if the blank is properly drawn into the die set, as the knockout retracts during the material formation process, the blank may be pulled slightly backwards. Worn knockouts and bushings tend to pull the material even further back, and visibly off-center, which disrupts the formation process and can adversely affect the quality of the product formed.